This invention relates to new and useful improvements in manhole constructions.
A common type of manhole construction employs a base, an upright housing portion for supporting an upper frame and a removable cover. The housing portion has communication at the lower end thereof with one or more underground pipes and has inlet means for connection to service lines.
The height of the inlet is determined by the depth at which the service line is embedded in the ground. In general, the service lines are buried to only the depth required in order to minimize excavation, and thus in many installations the inlet is high up in the manhole. In order to protect workmen who may have to work in the manhole from fluid entering through the elevated inlet, it is customary to dam off a portion of the inlet and to install an outside drop. such outside drop employs a tee connection outside of the manhole wherein one portion of the tee is connected to the service line, another portion of the tee is connected to the inlet in the manhole, and a third portion of the tee extends downward for connection to suitable outside conduit means encased in concrete and having an elbow directed into the manhole adjacent to the bottom of the latter.
These outside drops have the disadvantage that they add considerable expense to the manhole construction. In addition, in the event of poor ground support and other factors, breaking of the encasing concrete and shearing of the conduit often takes place and leakage thus occurs. Another disadvantage of outside drops is that they are difficult to clean.